From: =?iso-8859-1?Q?VIGILANT_Luis_Fern=E1ndez?= <luis@vigilant.es>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz:
 EA5DOM received)
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Date: Sat, 27 Oct 2018 21:11:54 +0000
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Subject: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz:
 EA5DOM received)
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Hi All, LF

Interesting topic. Also happens in MF but in LF it gets more critical. Must=
 be a nightmare at VLF :(

As Marco explained, our setup is not the usual at ground level in a propert=
y plot. And in my case ther ground
is 80m away down from the feed point, coil and capacitive topload.

Measured with the antenna analyzer I can see a drop in the impedance module=
 when all gets wet by rain
It is not only an increase of RF current. Today I measured resistance from =
the ground side of the feed point
trought the pipe to building basement and then returning via the water grid=
 connecting the other side of the
multimeter to a water pipe in my house:

4 Ohm measured early morning when it started with soft rain. At noon we had=
 stronger rain and in the afternoon
I measured again. It dropped to 2 Ohm. Big difference. Something gets wet i=
n the basement and the pipe gets
a better connection to ground, or at least to the water grid pipes, which f=
inally run underground

The top of the antenna is dismantled during storms, so can't measure impeda=
nce with the analyzer right now
but bet it is now well under 30 Ohm and would drain a few amps

Other intringuin detail. When it is dry and impedance rises to >100 Ohm the=
 only way to hardly reach 1A RF
is to detune the antenna. I have to set the resonant peak at 138Khz and the=
n at 137,5 get even higher impedance
and high SWR, but the antenna current rises and so the radiated signal. All=
 this at the cost of more amps
consumed by the PA and higer voltage at antenna feed. Running the antenna a=
t the optimum resonance makes
almost no RF current, even considering that this is the minimum impedance p=
oint.

About the LPF, this is really the only part of the Ropex PA still in use. T=
his is a link to the schematic with the LPF
https://www.dropbox.com/s/ejn5stuz7vban7u/Ropex%20Schematic.JPG?dl=3D0

Have not tried without LPF. The analyzer measurements are made directly to =
antenna. But may be a good idea to
make them with the LPF inserted and see what happens

73 de Luis
EA5DOM

________________________________
De: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org]=
 en nombre de marcocadeddu@tin.it [marcocadeddu@tin.it]
Enviado: s=E1bado, 27 de octubre de 2018 18:12
Para: rsgb_lf_group@blacksheep.org
Asunto: R: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM=
 received)

Hi Paul, Luis, Markus, LF

let me join the topic ;-)
the antenna location of Luis is something else of your Markus and Paul and =
much similar to mine: roof based antennas with elevated ground (in my case)=
 and vertical ground (the water pipe) for Luis.
Anyway also in my case the serie resistance of my antenna increases with ra=
in (almost doubles).
But.. Luis, probably assumes the lower impedance basing on the higher curre=
nt.
Luis, what kind of LPF have you adopted?
Now I have a T filter with no shunting cap at the input and impedance incre=
ases with rain both with and without LPF, but if I remember correctly, when=
 in the past I had an PI LPF with shunting input and output caps the impeda=
nce in my shack was transformed from the transmission line and LPF giving l=
ower impedance by rain.

Could be an explication?

By the way, just for fate it's raining also here and I made some measuremen=
t when dry again will repeat ;-)

Have a funny weekend LF

Marco IK1HSS


----Messaggio originale----
Da: paul@n1bug.com
Data: 27-ott-2018 12.34
A: <rsgb_lf_group@blacksheep.org>
Ogg: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM recei=
ved)

Hi Luis, Markus, LF

This is a very interesting topic for me too.

My antenna resistance is very high, usually more than 100 ohms. I
think there may be a few reasons. There are trees near the antenna
which I presume to be lossy. My antenna ground system is not tied
into the house ground, in order to minimize 120 Hz sidebands on my
transmitted signal. When I tie the grounds together the level of
these sidebands increases almost 20 dB. Also my RX antenna is more
noisy when the TX antenna ground and house ground are tied together.
I suppose this is because more noise is radiated from the TX
antenna, then picked up by the RX antenna which has its own small,
isolated ground.

Rain has no effect on the antenna resistance, but temperature does.
During summer there is little change, just minor variations. But as
the temperature drops and begins to approach freezing, resistance
begins to get lower. There is a big drop right around freezing or
few degrees below, but resistance continues to drop with even lower
temperatures, reaching minimum on the coldest winter nights. Last
winter I saw it reach 40 ohms a few times. :)

I am no expert but I guess the trees are partly responsible for the
high resistance and the drop with freezing temperature?

Anyway I can run enough power to reach calculated 1W EIRP and it's
enough to be heard across that little pond. :)

But here is a related question: I have calculated my EIRP to be one
watt using the measured resistance, antenna parameters and current.
But does this calculation include all the losses in trees? If I had
the proper equipment to make field strength measurements at a
distance, would I find that my EIRP is less than one watt due to the
tree losses?

73,
Paul N1BUG


On 10/27/18 5:45 AM, Markus Vester wrote:
> Hi Luis,
>
>> Impedance drops a lot after rain
>
> This seems unusual. I have exactly the opposite effect here:
> Series resistance at 137 kHz is normally around 20 ohms
> (including 5 ohms for the coil). When it rains it get worse up to
> about 40 ohms, whereas best times are cold and dry winter days
> with ~15 ohms when the trees are solidly frozen. So I presume
> that the major contribution to my resistance are
> capacitively-coupled losses in vegetation and other nearfield
> environment. The ground connection itself (the "house earth"
> which is connected to electric grid PE, and also pipe systems for
> water supply and distict heating) seems to have a low resistance.
>
>
> My only explanation for lower wet resistance would be if one were
> using a separate radial system in the garden, whose connection to
> ground might be better when the lawn is soaked. But I don't think
> this applies to your setup at all.
>
> Best 73, Markus
>
> Von: VIGILANT Luis Fern=E1ndez
>
> I'm struggling
> here with the antenna. Most of the time impedance rises and I
> hardly run 1A RF current
>
> Rainy weekend here.
> Impedance drops a lot after rain. Let's see how much current can
> drainLast time I could see almost 4A RF.


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<div style=3D"direction: ltr;font-family: Tahoma;color: #000000;font-size: =
10pt;">Hi All, LF
<div><br>
</div>
<div>Interesting topic. Also happens in MF but in LF it gets more critical.=
 Must be a nightmare at VLF :(</div>
<div><br>
</div>
<div>As Marco explained, our setup is not the usual at ground level in a pr=
operty plot. And in my case ther ground</div>
<div>is 80m away down from the feed point, coil and capacitive topload.</di=
v>
<div><br>
</div>
<div>Measured with the antenna analyzer I can see a drop in the impedance m=
odule when all gets wet by rain</div>
<div>It is not only an increase of RF current. Today I measured resistance =
from the ground side of the feed point</div>
<div>trought the pipe to building basement and then returning via the water=
 grid connecting the other side of the</div>
<div>multimeter to a water pipe in my house:</div>
<div><br>
</div>
<div>4 Ohm measured early morning when it started with soft rain. At noon w=
e had stronger rain and in the afternoon</div>
<div>I measured again. It dropped to 2 Ohm. Big difference. Something gets =
wet in the basement and the pipe gets</div>
<div>a better connection to ground, or at least to the water grid pipes, wh=
ich finally run underground</div>
<div><br>
</div>
<div>The top of the antenna is dismantled during storms, so can't measure i=
mpedance with the analyzer right now</div>
<div>but bet it is now well under 30 Ohm and would drain a few amps</div>
<div><br>
</div>
<div>Other intringuin detail. When it is dry and impedance rises to &gt;100=
 Ohm the only way to hardly reach 1A RF</div>
<div>is to detune the antenna. I have to set the resonant peak at 138Khz an=
d then at 137,5 get even higher impedance</div>
<div>and high SWR, but the antenna current rises and so the radiated signal=
. All this at the cost of more amps</div>
<div>consumed by the PA and higer voltage at antenna feed. Running the ante=
nna at the optimum resonance makes</div>
<div>almost no RF current, even considering that this is the minimum impeda=
nce point.&nbsp;</div>
<div><br>
</div>
<div>About the LPF, this is really the only part of the Ropex PA still in u=
se. This is a link to the schematic with the LPF</div>
<div><a href=3D"https://www.dropbox.com/s/ejn5stuz7vban7u/Ropex%20Schematic=
.JPG?dl=3D0" target=3D"_blank" style=3D"font-size: 10pt;">https://www.dropb=
ox.com/s/ejn5stuz7vban7u/Ropex%20Schematic.JPG?dl=3D0</a></div>
<div><br>
</div>
<div>Have not tried without LPF. The analyzer measurements are made directl=
y to antenna. But may be a good idea to</div>
<div>make them with the LPF inserted and see what happens</div>
<div><br>
</div>
<div>73 de Luis</div>
<div>EA5DOM</div>
<div><br>
<div style=3D"font-family: Times New Roman; color: #000000; font-size: 16px=
">
<hr tabindex=3D"-1">
<div id=3D"divRpF337372" style=3D"direction: ltr;"><font face=3D"Tahoma" si=
ze=3D"2" color=3D"#000000"><b>De:</b> owner-rsgb_lf_group@blacksheep.org [o=
wner-rsgb_lf_group@blacksheep.org] en nombre de marcocadeddu@tin.it [marcoc=
adeddu@tin.it]<br>
<b>Enviado:</b> s=E1bado, 27 de octubre de 2018 18:12<br>
<b>Para:</b> rsgb_lf_group@blacksheep.org<br>
<b>Asunto:</b> R: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz:=
 EA5DOM received)<br>
</font><br>
</div>
<div></div>
<div>Hi Paul, Luis, Markus, LF<br>
<br>
let me join the topic ;-)<br>
the antenna location of Luis is something else of your Markus and Paul and =
much similar to mine: roof based antennas with elevated ground (in my case)=
 and vertical ground (the water pipe) for Luis.<br>
Anyway also in my case the serie resistance of my antenna increases with ra=
in (almost doubles).<br>
But.. Luis, probably assumes the lower impedance basing on the higher curre=
nt.<br>
Luis, what kind of LPF have you adopted?<br>
Now I have a T filter with no shunting cap at the input and impedance incre=
ases with rain both with and without LPF, but if I remember correctly, when=
 in the past I had an PI LPF with shunting input and output caps the impeda=
nce in my shack was transformed
 from the transmission line and LPF giving lower impedance by rain.<br>
<br>
Could be an explication?<br>
<br>
By the way, just for fate it's raining also here and I made some measuremen=
t when dry again will repeat ;-)<br>
<br>
Have a funny weekend LF<br>
<br>
Marco IK1HSS<br>
&nbsp;<br>
<br>
----Messaggio originale----<br>
Da: paul@n1bug.com<br>
Data: 27-ott-2018 12.34<br>
A: &lt;rsgb_lf_group@blacksheep.org&gt;<br>
Ogg: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM recei=
ved)<br>
<br>
Hi Luis, Markus, LF<br>
<br>
This is a very interesting topic for me too.<br>
<br>
My antenna resistance is very high, usually more than 100 ohms. I<br>
think there may be a few reasons. There are trees near the antenna<br>
which I presume to be lossy. My antenna ground system is not tied<br>
into the house ground, in order to minimize 120 Hz sidebands on my<br>
transmitted signal. When I tie the grounds together the level of<br>
these sidebands increases almost 20 dB. Also my RX antenna is more<br>
noisy when the TX antenna ground and house ground are tied together.<br>
I suppose this is because more noise is radiated from the TX<br>
antenna, then picked up by the RX antenna which has its own small,<br>
isolated ground.<br>
<br>
Rain has no effect on the antenna resistance, but temperature does.<br>
During summer there is little change, just minor variations. But as<br>
the temperature drops and begins to approach freezing, resistance<br>
begins to get lower. There is a big drop right around freezing or<br>
few degrees below, but resistance continues to drop with even lower<br>
temperatures, reaching minimum on the coldest winter nights. Last<br>
winter I saw it reach 40 ohms a few times. :)<br>
<br>
I am no expert but I guess the trees are partly responsible for the<br>
high resistance and the drop with freezing temperature?<br>
<br>
Anyway I can run enough power to reach calculated 1W EIRP and it's<br>
enough to be heard across that little pond. :)<br>
<br>
But here is a related question: I have calculated my EIRP to be one<br>
watt using the measured resistance, antenna parameters and current.<br>
But does this calculation include all the losses in trees? If I had<br>
the proper equipment to make field strength measurements at a<br>
distance, would I find that my EIRP is less than one watt due to the<br>
tree losses?<br>
<br>
73,<br>
Paul N1BUG<br>
<br>
<br>
<br>
On 10/27/18 5:45 AM, Markus Vester wrote:<br>
&gt; Hi Luis,<br>
&gt; <br>
&gt;&gt; Impedance drops a lot after rain<br>
&gt; <br>
&gt; This seems unusual. I have exactly the opposite effect here:<br>
&gt; Series resistance at 137 kHz is normally around 20 ohms<br>
&gt; (including 5 ohms for the coil). When it rains it get worse up to<br>
&gt; about 40 ohms, whereas best times are cold and dry winter days<br>
&gt; with ~15 ohms when the trees are solidly frozen. So I presume<br>
&gt; that the major contribution to my resistance are<br>
&gt; capacitively-coupled losses in vegetation and other nearfield<br>
&gt; environment. The ground connection itself (the &quot;house earth&quot;=
<br>
&gt; which is connected to electric grid PE, and also pipe systems for<br>
&gt; water supply and distict heating) seems to have a low resistance.<br>
&gt; <br>
&gt; <br>
&gt; My only explanation for lower wet resistance would be if one were<br>
&gt; using a separate radial system in the garden, whose connection to<br>
&gt; ground might be better when the lawn is soaked. But I don't think<br>
&gt; this applies to your setup at all.<br>
&gt; <br>
&gt; Best 73, Markus<br>
&gt; <br>
&gt; Von: VIGILANT Luis Fern=E1ndez<br>
&gt; <br>
&gt; I'm struggling<br>
&gt; here with the antenna. Most of the time impedance rises and I<br>
&gt; hardly run 1A RF current<br>
&gt;<br>
&gt; Rainy weekend here.<br>
&gt; Impedance drops a lot after rain. Let's see how much current can<br>
&gt; drainLast time I could see almost 4A RF.<br>
<br>
<br>
<br>
</div>
</div>
</div>
</div>
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